Water tank



FIG. 1 is a perspective view of a water tank showing my new design;

FIG. 2 is a front elevational view thereof;

FIG. 3 is a rear elevational view thereof;

FIG. 4 is a left side elevational view thereof;

FIG. 5 is a right side elevational view thereof;

FIG. 6 is a top plan view thereof; and,

FIG. 7 is another perspective view thereof, with the toilet bowl engaged.

The dotted line showing of the toilet bowl is for illustrative purposes only and forms no part of the claimed design. 

The ornamental design for a water tank, as shown and described. 